Devices for automatically plotting a progression of positions in relation to a map or other representation of a navigational chart are well-known. For example, U.S. Pat. No. 4,468,743 (Dunn et al.) discloses a plotting device which is controlled by a microelectronic processor. The microelectronic processor drives a pen across a paper chart which is replaced after several plots. The Dunn et al. devices are best suited for a stable or sheltered environment which is inconsistent with the needs in smaller sailing vessels.
A more recent development in the field of navigational plotting systems is disclosed in U.S. Pat. No. 4,862,374 (Ziemann). The system disclosed therein includes a light-transmissive LCD graphical display. The light-transmissive graphical display serves as a window-like element in relation to a map or chart which is placed underneath it. The map or chart is calibrated to the plotter by moving a calibration cursor on the display to two known points which are diagonally displaced on the map and by entering the latitude and longitude of the known positions. Navigational positions are then related to these points and displaced at the appropriate locations on the display, i.e., over the appropriate locations on the underlying map.
Other electronic chart displays for boats are available. However, such displays generally produce relatively small printouts which are difficult to read or entail a somewhat cumbersome system which is not suitable for smaller vessels, such as a sail boat or motor yacht. Accordingly, it is desirable to provide a system which enables an individual to use conventional navigational charts for navigation. At the same time, the system should coordinate or scale navigational information from a Loran or GPS (Global Positioning System) receiver to the same scale as used on the chart. After coordinating the incoming information, the system should display the information, i.e., the position of the vessel directly onto the chart and at the same time allowing the individual to manually plot courses directly on the chart.
It is presently believed that a navigational system in accordance with the present invention provides the aforementioned desirable features. Such systems are also relatively compact and therefore suitable for use on sailboats or other yachts. Such systems can also be marketed at a competitive price and are suitable for working in subdued lighting, which is a typical environment on sailboats.